Idle mixture adjustment



July 9, 1968 1. o. SARTO 3,391,909

IDLE MIXTURE ADJUSTMENT Filed Aug. lO, 1966 .Mw if f/ IN VENTO.

United States Patent O 3,391,909 IDLE MIXTURE ADJUSTMENT Jorma O. Sarto, Orchard Lake, Mich., assigner to Chrysler Corporation, Highland Park, Mich., a cor- -r poration of Delaware Filed Aug. 10, 1966, Ser. No. 571,506 6 Claims. (Cl. 261-41) ABSTRACT OF THE DISCLGSURE An idle mixture screw is provided with an extended tip that projects throughthe idle mixture fuel and -air orifice of a carburetor and into the fuel-air induction conduit at all operating positions of adjustment, thereby to limit the maximum idle fuel enrichment until engine idling is prohibited `by unscrewing the idle mixture screw completely from the carburetor.

This invention relates to means for adjusting the fuelair mixture for an internal combustion engine at idle and has -for an important object the provision of an improved idle mixture adjusting screw to prevent excessive enrichment of the fuel in the mixture.

In conventional carburetors for an internal combustion engine, an idle fuel port located downstream of the throttle valve in lthe customary fuel-air induction conduit supplies ya fuel-air mixture adequate to support engine operation during idling. An idle adjustment screw adjustably screwed into the sidewall of the induction conduit from the latters exterior terminates inwardly in a conically inwardly tapered valve element aligned with the upstream side of the idle fuel port to adjust its effective opening. Thus, by unscrewing the idle adjustment screw, the conical valve element is withdrawn outwardly from the idle fuel port to open the latter.

During operation of the engine at the idle condition, the throttle valve is substantially closed and the resulting low pressure in the induction conduit downstream of the' throttle valve induces uid flow through the idle fuel system and into the induction conduit via the idle fuel port. When the latter is substantially closed by virtue of the idle adjustment screw being screwed inwardly, the pressure drop across the idle fuel port is at a maximum because the tendency to bleed air into the induction conduit through the idle fuel Vport and thereby to reduce the pressure in the idle fuel system upstream of the idle fuel port is compensated for by bleeding air into the idle system through the conventional restricted idle transfer and idle air bleed ports. Thus substantially atmospheric air pressure is maintained in the idle fuel system upstream of the idle fuel port.

As the idle adjustment screw is progressively unscrewed to open the idle fuel port during engine idling, the restricted idle transfer and air bleed ports cannot supply suiiicient air to maintain the pressure upstream of the idle fuel port, 'and said pressure is progressively reduced. In consequence the idle fuel ow into the idle fuel system from the conventional idle fuel supply port is progressively increased, such that `the idle fuel-air mixture discharged into the induction conduit is progressively enriched with fuel with respect to the combustion supporting air supplied by leakage around the throttle valve and via the aforesaid idle transfer and air bleed ports. In many carburetor constructions, the idle fuel-'air mixture can be enriched excessively by unscrewing or opening the idle mixture screw to the extent that combustion of the mixture in the engine is incomplete and objectionable unburned hydrocarbons are exhausted.

It is accordingly another and more specific object of the present invention to provide simple and inexpensive 3,391,909 Patented July 9, 1968 ICC means lfor limiting the idle fuel enrichment and to prevent accidental over enrichment of the idle fuel-air mixture, comprising an idle adjustment screw of generally conventional construction land including in laddition an inward cylindrical extension of the conical valve element. The cylindrical extension projects through the idle fuel port and into the induction conduit to such an extent that it will yrestrict the maximum effective opening of the idle port until the idle adjustment screw is unscrewed at least sufficiently from the sidewall of the induction conduit to enable leakage of air around the -body of the screw and into the idle fuel system at the upstream side of the idle fuel port to prevent further idle enrichment; and preferably until the idle adjustment screw is unscrewed e11- tirely from the induction conduit sidewall, in which event the screw will fall from its screw hole and the inflow of air therethrough will cut off the idle fuel and prevent engine idling.

lOther objects of this invention will appear in the following description and appended claims, reference being had to the laccompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

FIG. 1 is a somewhat schematic vertical sectional view through a carburetor embodying the present invention, taken through the air induction conduit and idle fuel system.

\FIG. 2 is an enlarged sectional view showing details of the idle adjust-ment screw as in FIG. -1.

FIG. 3 is -a view similar to FIG. 2, but showing the adjustment screw at the limit of its unscrewed or open position.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Referring in more particularity to the drawings, a carburetor is illustrated comprising three principal body sections including an upper air inlet and choke valve section 10, yan intermediate venturi section 11, and a lower throttle section 12 suitably spaced -by gaskets and bolted together by means not specifically shown. The three carburetor sections cooperate to define an induction conduit 13 extending completely therethrough and adapted to align with 'a customary intake header `for conducting a combustible fuel and air mixture to the engine.

The intermediate body portion 11 is formed with large venturi 14 aligned coaxially with the conduit 13 and seprated from an integral fuel bowl section 15 by means of a transverse vertical wall 16. The fuel bowl 15 contains a supply of liquid fuel automatically maintained at approximately the level 17 by a oat controlled inlet valve connected with a customary fuel pump. The top of the fuel bowl 15 is covered by an extension 18 of the upper body section 10 to provide a comparatively dust free fuel bowl enclosure which is vented by means of vent duct 18a to atmospheric pressure within conduit 13 above the conventional choke valve described below.

A throttle valve rod 19 is pivotally mounted in the conduit portion 13 of the throttle body section 12 and supports a throttle valve 20 operable in a conventional manner by a pedal actuated linkage. The lower body portion 12 is also formed with mounting flanges 21 to facilitate mounting of the carburetor assembly on the intake manifold as aforesaid.

An embossment 22 of the transverse wall 16 extends to the right to define a portion of the venturi 14 and is -28 pressed tightly therein and discharging into the throat l region of the venturi 24. The upper end of the passage 27 communicates with the upper portion of the well 23 for receiving fuel therefrom during operation of the engine under load. l

A hollow vent or partitioning tube 30 is secured within the recess- 26 by means of a press fit and extends downwardly into the well 23. The tube 30 is formed with a .plurality of ports.,31 spaced along its length to permit the transfer of airl from its interior into the adjacent portions of the. well 23 for emulsifying the fuel. Air is ad- .mitted intothe hollow interior of the tube 30 at its upper end through a restricted port 32, which communicates with the air induction passage 13.

A second recess 33 is formed in the upper portion of the extension 25 to receive the upper end of an idle tube 34 pressed tightly therein. The idle tube 34 communciates with the bottom of the well 23 through an idle fuel inlet port 35 and communicates with a -third recess 36 in the upper end of extension 25 by means of an upper trans- A clamping bolt 39 is received snugly within the opening 36 and is screwed tightly into the opening 38 to clamp the projection 25 securely in place on the embossment 22. A fibrous gasket 40 is preferably disposed between the extension 25 and embossment 22.

The central bore of bolt 39 communicates upwardly through an idle air bleed restriction 41 with the air induction passage 13 to receive air for mixing with the idle fuel to provide a combustible fuel and air mixture for the engine during idling. This idle fuel-air mixture is conducted through the bolt 39 to a communicating idle fuel passage 42 which extends downwardly into the throttle body section 12 and opens into the induction conduit 13 through an inwardly tapered conical idle port 43 located downstream of the throttle valve 20. The degree of restriction of the idle port 43 may be varied by a mating conical valve element 44 having an integral coaxial screw threaded outer body 45 threadably connected to the lower .body 12 and extending to the exterior thereof to permit manual adjustment.

The interior of the fuel bowl section 15 contains a main metering element 46 screwed into the base of the fuel bowl at 47. The metering element 46 is situated substantially on the plane of symmetry of the fuel bowl and is formed with a main metering orifice 48 communicating with a fuel supply passage 49 which discharges into the bottom of the fuel well 23. The upper portion of the metering element 46 slidably receives and guides a meterpiston 51 is adjusted vertically within the cylinder 52 in response to the engine manifold pressure.

Cooperating with the idle fuel system is a vertically slotted idle transfer port 55 in communication with the idle conduit 42 and opening into the sidewall of the conduit 13. Preferably the transfer slot 55 extends upwardly from its lower end, located at approximately the upper edge of the throttle blade 20 when the latter is in the closed or idle position shown, toits upper end.sligh tl.y above the aforesaid upper edge of the throttle valve 20.

A choke rod 56 is pivotally mounted in the conduit portion 13 of the upper air horn or inlet section 10 and car-ries a pivotal unbalanced choke blade 57. The latter is urged to its closed positionwith fa force which increases with decreasing temperature byirneans ofba 'temperature controlled linkage comprising a duall crank'armfnember 58, connected with the chokeuro'd`56 to Vpivot therewith, and a link`59'. The'dualv crank arm. "rnenibe'rl 58 has an interior ar-m extending radially frni'rod 56 within conduit 13 and an exterior arm extending radially from rod 56 exteriorly of conduit 13. The link 59 is-pivotally connected at its upper end with the outer end of the: exterior arm of crank arm member 58 and is connected at lits lower end with the free end of a'bimet'allic thermostatic 'spring-60. 'M

' The lfixed'end 61 of ithe latter is secured'wit'hina'ho'u'sing portion'y 62 responsive to a' suitable engine foperati'ng temperature, so that as thev engine temperature rises, the thermostatic spring force urging closing -ofth'ef choke valve 57 decreases. Also pivotally connected to the outer swinging end of the interior arm of crank arm member 58 is 'a link 63:'pivotally connected at its opposite end with a reciprocal plunger 64 which extends through a sidewall opening 66 in the upper body section 10and is suitably secured at its outer end'by clamping'plates 67 to a flexible diaphragm 68. The latter is urged leftward in'the drawing by means of a biasing spring 69, so as to urge the choke valve 57 to theclosed positionillustrated in dotted lines. The diaphragm 68 defines one wall ofa pressure chamber 70 which is connected by means of aconduit 71 vwith the induction'conduit 13 to a location downstream of the throttle valve 20. In the present instance the chamber 70 is also defined in part by a housing 72 having lfootings' 73 secured to body section 10.

Thestructur'e described thus far may relate 'to either a single or multiple barrel carburetor and may be conventional, reference being had to Ball Patent No. 2,966,-

344 and to Sarto copending application Ser. No. 368,193, now Patent No.'3,290,023, as if the same were-incorpo- `r'ated'herein, for a more complete discussion of the structure and operation of the conventional details shown. In operation, the fuel well 23 tends to be partially filled with fuel to the level 17'by means of the metering vorifice A48 and conduit 49. When the throttle valve 20 is at the 'closed or idle position-shown, the low pressure down- 'stream of the valve 20 will actuate diaphragm 68 to pull 4the choke valve 57 to the partially open position shown against the closing. force of the thermostatic spring'r60,

Also the low vpressure downstream of the throttle valve 20 will actuatepiston 51 and pull the '.latterand plunger 50 downwardly to the idle position, so as'to restrict the opening 48 in accordance with the idle operating conditions. The low pressure downstream yofthrottle valve'20 induces uid lflow via idle conduit 42 and port 43 into the'induction conduit, whereupon fuel in the well 23 is forced upwardly through the idle. tube.34'via idle supply `port-35 tothe. duct 37 land thence into the-bore of the hollow lbolt 39 .and downwardly into the conduit 42.

Similarly, air for supporting idle combustion will be supplied-by controlled leakage around the throttle valve 20,' through therestricted vent 41, and through the .transfer port 55, which latter will be inthe high pressure region of the conduit ,13 by virtue of thepartially open choke, and thence via conduit 42 and port 43 into th induction conduit 13 to support engine idling.4 .v

As the throttle is initially opened progressively in accordance with increased engine load, the portion of the transfer port 55 downstream of the upper edge ofthe throttle blade 20 will progressively increase, thereby to decrease the pressure in idle conduit 42 and increase the fuel flow therethrough from idle tube 34 and into conduit -13 via both ports 55 and 43. As the throttle 20 continues to open to increase the air iiow in conduit 13, low pressure will be induced at the lower end of nozzle 28 by reason of the venturi system 14, 24 and fuel will be forced upwardly in Well 23 to passage 27 and discharged via nozzle 28. Simultaneously, emulsifying air for the main fuel supply will be admitted into tube 30 via restriction 32 and admixed with the fuel in well 23 by means of ports 31. Finally, after continued opening of throttle 20, the pressure in conduit 13 at the ports 43 and 55 will rise sufficiently to prevent fuel iiow in the idle system. As the air ow in conduit 13 increases, the air impinging against the unbalanced choke blade 57 will force the latter open regardless that the increased pressure at the right of diaphragm 68 no longer urges opening of the choke valve 57. Also with the increasing pressure downstream of throttle 20 as the latter progressively opens, the metering rod 50 will be wtihdrawn from metering port 48 to progressively open the latter and increase the fuel flow into well 23.

Referring in more particularity to FIGS. 2 and 3, the idle valve 44 extends inwardly from screw 45 and terminates inwardly in an integral coaxial cylindrical nose or extension 74.

By reason of the extension 74 which has approximately the diameter of the smaller end of conical valve element 44 and which extends freely through the smaller end of the conical port 43 with suflicient clearance to enable a predetermined minimum restriction for maximum fuel enrichment when the screw 45 is unscrewed approximately to the position shown in FIG. 2, further unscrewing of screw 45 will not decrease the effective restriction for port 43. Thus the maximum idle fuel enrichment can be predetermined.

In the above regard, during engine idling, as the screw body 45 is unscrewed to decrease the restriction of the idle port 43, the pressure in duct 42 will decrease by reason of the restricted nature of vent 41 and transfer port 55. An increased quantity of idle fuel will thus be forced upwardly through idle tube 34 and thence into the idle conduit 42 for discharge via port 43 into the induction conduit 13, thereby to enrich the fuel-air mixture. The converse obviously occurs by tightening the screw 45 so as to moxe the valve portion 44 rightward to increase the restriction of idle port 43. An idle adjustment spring 75 under compression between the head of screw 45 and the sidewall of the conduit section 12 serves to urge the screw 45 outwardly and also to maintain the latter in its adjusted position.

Without the provision of nose 74, an attempt to enrich the idle fuel-air mixture could result in excessive enrichment and in the exhaust of unburned hydrocarbons. The elongated cylindrical nose 74 however extends through the idle port 43 into the induction conduit 13 to such an extent that the maximum enrichment through idle port 43 is limited regardless of how far screw 45 is unscrewed. Thus when screw 45 is unscrewed to the maximum extent permissible, i.e., just before the screw 45 is completely unscrewed and falls from the mating screw hole in throttle body 12, FIG. 3, the cylindrical extension 74 will still afford adequate restriction for the idle metering port 43 to prevent excessive enrichment of the idle fuel mixture. If the screw 45 is then unscrewed beyond the aforesaid limit, the spring 72 will push the screw 45 completely from its mating screw hole, thereby to open the idle conduit 42 to the atmosphere and entirely eliminate the induction of idle fuel into the idle system.

Having thus described my invention, I claim:

1. In a fuel charging means for an internal combustion engine, a fuel-air induction conduit, means for supplying fuel to said conduit including an inner metering port opening into said conduit through a sidewall thereof, an outer opening in said sidewall for connecting said port with the exterior of said conduit, adjustable valve means mounted in said sidewall for adjusting movement in inward and outward directions with respect to said conduit, said valve means comprising a valve element for adjustably restricting said port upon said movement and also comprising an outer body adjustably seated within said outer opening for closing the same and the connection between said port and said exterior, said outer body being movable outwardly to unseat from within said outer opening for opening the same and connecting said port With said exterior upon predetermined outward movement of said valve means, and means for limiting the maximum opening of said port into said conduit upon said predetermined outward movement of said valve means comprising an inner extension of said valve element projecting inwardly through said port and into said conduit sufliciently that a portion of said inner projection Will remain in said port to partially restrict the latter upon said predetermined outward movement of said Valve means to unseat said outer body from said outer opening.

2. In the combination according to claim 1, the sidewall of said conduit having portions engaging said outer body only when the latter is seated within said outer opening to retain said valve means in its adjusted position, and means yieldingly holding said Valve means in adjusted position within said outer hole.

3. In the combination according to claim 1, said inner port and outer opening being coaxial and said outer body being in screw threaded engagement with the sidewall of said conduit when seated within said outer opening and being unscrewed from said sidewall When unseated from within said opening.

4. In the combination according to claim 3, resilient means yieldingly urging said valve means outwardly to hold said outer body in adjusted position within said outer opening.

5. In the combination according to claim 4, said valve element being conically tapered coaxially inwardly with respect to said inner port and said inner extension comprising a coaxial cylinder having a diameter on the order of magnitude of the minimum diameter of said tapered valve element.

6. In the combination according to claim 4, a throttle valve in said conduit, said inner port comprising an idle port downstream of said throttle for supplying a fuel-air mixture to said engine during idling thereof, and said valve body comprising an idle mixture adjustment screw integral With said valve element and inner extension.

References Cited UNITED STATES PATENTS 2,618,473 ll/ 1952 Whitford.

FOREIGN PATENTS 1,429,365 1/ 1966 France.

HARRY B. THORNTON, Primary Examiner. TIM R. MILES, Examiner. 

